Health officials and water administrators stand before the television cameras to announce important news: Tests have found E. coli in the water supply. Boil it, but don't panic.

If the scenario sounds familiar, that's because it happened just two years ago, on Saturday, July 21, 2012.

Portland has issued two boil-water alerts before the one today, May 23, 2014. Like today's alert, the previous two involved E. coli contamination, although both were much smaller in scope than the current one.

The first in Portland history came Saturday, Nov. 28, 2009. The city urged 50,000 business and residential customers in Portland west of the Willamette River to boil water. The alert also covered the smaller Valley View, Burlington and Palatine Hill water districts.

Triggering the alert was a positive test for E. coli at Reservoir 3 in Southwest Portland's Washington Park, a 16.4-million-gallon reservoir built in 1894. A gravity-powered system delivers water from Mount Tabor Park's Reservoir 5 to Washington Park's Reservoir 3.

Restaurants on Portland's westside tossed out ice, quit serving water and coffee or closed, and hotels offered guests bottled water and apologies.

Washington Park Reservoir 3 was again the culprit in 2012. That time, 135,000 households on the westside were hit with the order. Also affected were: the Burlington, Valley View, Palatine Hills, Lake Grove and West Slope water districts; and the city of Tigard.